The chemistry, synthesis and biological activity of N-Phosphorylated amino acid is being studied. Pseudomonas phaseolicola, the bacterial pathogen of Phaseolus vulgaris produces a family of compounds, phaseotoxins. Phaseotoxin A appears to be N-Phosphoro glutamic acid. Both the naturally occurring compounds and synthetic N-P glutamate inhibit an important urea cycle enzyme, ornithine carbamoyl transferase (OCT). We have found that inorganic phosphate interferes with phaseotoxin inhibition of OCT by a complicated mechanism. Treatment of inoculated P. vulgaris tissues with low concentrations of Pi apparently renders the OCT of such tissues incapable of being inhibited by phaseotoxins, which are produced by the pathogen in infected tissues. Pi treated plants recover from chlorosis which is the result of OCT inhibition; the exact biochemical mechanism of this is not yet understood. Phaseotoxins also appear to be involved in the specificity of the pathogen for its host. The toxins suppress the resistance response of the host tissues incited specifically by the P. phaseolicola-P.glycinea group but not by several other phytopathogenic pseudomonads.